I really wasn't expecting a lot from the multiplayer, don't see why so many of the achievements have to be from that. I think with most 360 games coming out now the developers might feel that they have to add a multiplayer mode to keep up with the rest of the 360s games, particularly most shooting/action games. I really hate then that happens, because the multiplayer seems to be a let down in most cases. Anyway, the sinle player mode does look awesome, I think I'll still end up buying it.
If you could, when your comeplete the single player let me know rouhgly how long it is, I might even just rent this game rather than buy it.